Magneto-optical pickup

ABSTRACT

A pickup includes a light source for emitting a light beam that travels to an information recording medium along a first optical path, a first light receiving element group for detecting an error signal, a second light receiving element group for detecting a magneto-optical signal, a diffraction grating for diffracting light returned along the first optical path, a polarization beam splitter for separating a part of the return light such that a beam of the return light travels to the second light receiving element group along a second optical path, a mirror for bending the second optical path so that a light beam reflected thereby is directed toward the second light receiving element group, and an anisotropic crystal member that has an optic axis inclined between 30° and 60° and that includes a substantially parallel flat plate portion between the mirror and the first light receiving element group.

[0001] This application is a Continuation of application Ser. No.09/695,083 filed Oct. 24, 2000.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 11-310144, filed Oct. 29,1999, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0003] The present invention relates to an optical device for opticallyprocessing information by light beam scanning, and more particularly, toa magneto-optical pickup for detecting magneto-optical signals.

[0004] Recently developed magneto-optical pickups are designed so that aplurality of functions and elements are integrated to ensure smallersizes and lower costs.

[0005] Jpn. Pat. Appln. KOKAI Publication No. 8-329544 discloses asmall-sized magneto-optical pickup, which is schematically shown in FIG.12.

[0006] In FIG. 12, a beam of laser light emitted from a semiconductorlaser 17 is transmitted through a polarizing prism 23 and converged onan information storage medium 26 by an objective lens 25.

[0007] The beam of laser light including information, which is reflectedby the information storage medium 26, is split into two by a surface 23a of the polarizing prism 23 in accordance with the polarization. Lightcomponents transmitted through the surface 23 a are diffracted by aholographic diffraction element 22 and then detected as focus andtracking error signals by light receiving elements 18 and 19 on asubstrate 16.

[0008] On the other hand, a beam of light components reflected by thesurface 23 a is deflected by a mirror surface 23 b, and then split intotwo by a prism-type analyzer 24, which includes a plurality of prismsand a polarizing film, located on the substrate 16. The split beams aredetected as magneto-optical signals by a light receiving element group20.

[0009] The light receiving elements 18 and 19 and the light receivingelement group 20 are all formed on the same substrate 16, and the laserlight source 17 is also mounted on the substrate 16. The substrate 16,along with the prism-type analyzer 24, is sealed mainly in a small-sizedresin package.

[0010] Jpn. Pat. Appln. KOKAI Publication No. 8-329544 also teaches amethod for detecting magneto-optical pickup signals by using apolarizing diffraction element in stead of the prism-type analyzer 24,with a beam of light including information split into three beams of 0thand p1st order diffracted light.

[0011] Further, Jpn. Pat. Appln. KOKAI Publication No. 10-143934disclosed an improved magneto-optical pickup based on an additionallydeveloped technique, which is schematically shown in FIG. 13.

[0012] In FIG. 13, a laser beam emitted from a laser diode 3 istransmitted through a polarizing prism 9 and converged on an informationstorage medium 13 by a objective lens 12.

[0013] The laser beam reflected by the information storage medium 13 issplit into two by a surface 9 a of the polarizing prism 9 in accordancewith the polarization. Light components transmitted through the surface9 a are diffracted by a holographic diffraction element 8 and detectedas error signals, such as focus and tracking error signals, by lightreceiving elements 4 and 5 on a substrate 2.

[0014] On the other hand, a beam of light components reflected by thesurface 9 a is deflected by a mirror surface 9 b, and then split intotwo beams in accordance with the polarization by a Wollaston prism 10,which is united with the polarizing prism 9. The split beams aredetected as magneto-optical signals by a light receiving element group6.

[0015] The light receiving elements 4 and 5 and the light receivingelement group 6 are all formed on the same substrate 2, and the laserlight source 3 is also mounted on the substrate 2. The substrate 2 issealed mainly in a small-sized resin package.

[0016] Using the prism-type analyzer for the separation of themagneto-optical signals, the magneto-optical pickup shown in FIG. 12includes a very large number of components. Further, each componentrequires high working accuracy, and its assembly also requires highaccuracy.

[0017] In particular, mounting the prism-type analyzer itself on thesubstrate requires very high accuracy, and naturally, mounting thepolarizing prism for guiding light to the analyzer also requires highaccuracy. If the mounting accuracy of the analyzer 24 is unsatisfactory,therefore, adjustment cannot be carried out when the polarizing prism 23is mounted, in some cases. If the mounted analyzer is concluded to bedefective by inspection after assembly, therefore, the semiconductorlaser, light receiving element substrate, and package, which are ratherexpensive, must possibly be scrapped.

[0018] Use of the polarizing diffraction element for separation of themagneto-optical signals also requires high working and mountingaccuracies. Further, the polarizing diffraction element itself is veryexpensive. Since a light beam is split at angles by the diffractionelement, in particular, the distances between the diffraction elementand the light receiving element group must be adjusted and maintainedwith high accuracy. Partly because the package is formed mainly ofresin, moreover, the resulting pickup is susceptible to change of theenvironmental conditions.

[0019] The magneto-optical pickup shown in FIG. 13 entails highmanufacturing cost, since it uses the very expensive Wollaston prism forthe separation of the magneto-optical signals. This pickup, like theforegoing magneto-optical pickup, moreover, requires high mountingaccuracy.

[0020] Since the Wollaston prism deflects beams in ordinary andextraordinary rays in different directions, in particular, high mountingaccuracy is needed to focus spots correctly on the light receivingelements. Further, fluctuations of the distance between the Wollastonprism and the light receiving element substrate prevent the spots frombeing focused correctly on the light receiving elements. Since thepackage is formed mainly of resin, this magneto-optical pickup issusceptible to change of the environmental conditions. In order tosecure a long distance of separation between the beams in ordinary andextraordinary rays, furthermore, the space between the Wollaston prismand the light receiving element substrate should be adjusted to acertain dimension. Accordingly, the size of the pickup can be reducedonly limitedly.

[0021] Thus, according to the conventional magneto-optical pickups, alot of components or expensive parts must be assembled with very highaccuracy.

BRIEF SUMMARY OF THE INVENTION

[0022] The object of the present invention is to provide amagneto-optical pickup, which requires relatively low mounting accuracyand is small-sized and low-priced.

[0023] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bythe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0024] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0025]FIG. 1 shows a magneto-optical pickup according to a firstembodiment;

[0026]FIG. 2 shows the inclination of an optic axis of a parallel flatplate shown in FIG. 1 with respect to the optical axis;

[0027]FIG. 3 shows a modification of the way of mounting a laser lightsource according to the first embodiment;

[0028]FIG. 4 shows a modification of the magneto-optical pickup of thefirst embodiment;

[0029]FIG. 5A is a plan view of a magneto-optical pickup according to asecond embodiment;

[0030]FIG. 5B is a sectional view of the magneto-optical pickup takenalong line 5B-5B of FIG. 5A;

[0031]FIG. 5C is a sectional view of the magneto-optical pickup takenalong line 5C-5C of FIG. 5A;

[0032]FIG. 6 shows the surroundings of a laser light source of amagneto-optical pickup according to a third embodiment;

[0033]FIG. 7 shows a modification of the magneto-optical pickup of thethird embodiment;

[0034]FIG. 8 shows a magneto-optical pickup according to a fourthembodiment;

[0035]FIG. 9 shows a packaged magneto-optical pickup according to afifth embodiment;

[0036]FIG. 10 shows a magneto-optical pickup according to a sixthembodiment;

[0037]FIG. 11 is a graph showing the way of generating a phasedifference according to the sixth embodiment;

[0038]FIG. 12 shows a prior art magneto-optical pickup; and

[0039]FIG. 13 shows another prior art magneto-optical pickup.

DETAILED DESCRIPTION OF THE INVENTION

[0040] Preferred embodiments of the present invention will now bedescribed with reference to the accompanying drawings.

[0041] First Embodiment

[0042] As shown in FIG. 1, a magneto-optical pickup according to a firstembodiment comprises a laser light source 31 for emitting a light beamfor information reproduction, a first light receiving element group,which includes light receiving elements 34 and 35, for detecting errorsignals, and a second light receiving element group 36 for detectingmagneto-optical signals. The light receiving elements 34 and 35 and thesecond light receiving element group 36 are formed on one siliconsubstrate 39, and therefore, are situated on a common plane. The laserlight source 31 is mounted on the silicon substrate 39 so that a lightbeam is emitted at right angles to the upper surface of the substrate39.

[0043] The laser light source 31 may be located at the bottom of arecess having a 450 slope, formed in the silicon substrate 39 byetching, for example, so that a light beam emitted from the light source31 parallel to the upper surface of the substrate 39 is deflected upwardby the 45° slope.

[0044] The magneto-optical pickup has a first optical path. The lightbeam emitted from the laser light source 31 travels to an informationstorage medium (not shown) along the first optical path. Arranged on thefirst optical path are a collimating lens for collimating the light beamand an objective lens for converging the light beam on the storagemedium. The direction of polarization of the light applied to thestorage medium is changed according to recorded information, and theresulting reflected light returns along the first optical path.

[0045] The magneto-optical pickup comprises a transparent flat plate 32having a diffraction grating 32 a for diffracting the light that returnsfrom the information storage medium along the first optical path. Beamsof diffracted light are directed toward the light receiving elements 34and 35, respectively.

[0046] The magneto-optical pickup has a second optical path, andcomprises a polarization beam splitter 33 for separating or deflectingpartial components of the light that returns from the informationstorage medium along the first optical path. The light componentsseparated or deflected by the beam splitter 33 travel to the secondlight receiving element group 36 along the second optical path. Thepickup further comprises a mirror prism 37 for bending the secondoptical path. The prism 37 serves to reflect the light components fromthe beam splitter 33, thereby directing them toward the second lightreceiving element group 36.

[0047] The magneto-optical pickup further comprises a parallel flatplate 38, which is located between the mirror prism 37 and the secondlight receiving element group 36. The plate 38 is of an anisotropicoptical crystal, and has an optic axis inclined to the optical axis, asshown in FIG. 2. An angle of inclination of the optic axis to theoptical axis is within the range between preferably 30° and 60°, andmore preferably between 40° and 50°, and most preferably 45°. Further,the optic axis of the parallel flat plate 38 is also inclined at about45° to the direction of polarization of the incident light.

[0048] In FIG. 1, the light beam emitted from the laser light source 31is transmitted through the transparent flat plate 32 having thediffraction grating 32 a and then through the polarization beam splitter33. Thereafter, the light beam is changed into a collimated light beamby the collimating lens (not shown) and converged on the informationstorage medium (not shown) by the objective lens (not shown).

[0049] The return light from the storage medium, including information,having passed through the objective lens and the collimating lens,reaches at the polarization beam splitter 33. Some components of thereturn light are reflected by a polarizing film 33 a of the polarizationbeam splitter 33, while the remaining light components are transmittedthrough the beam splitter 33.

[0050] The light components transmitted through the polarization beamsplitter 33 are diffracted by the diffraction grating 32 a, thereforetwo beams of −1st order diffracted light and +1st order diffracted lightappear. The light quantities of the −1st order diffracted light and +1storder diffracted light are detected by the light receiving elements 34and 35, respectively, each of which has light receiving regions dividedin given shapes or a plurality of light receiving elements. Based on thedetected quantities, focus error signals and tracking error signals aredetected.

[0051] On the other hand, a beam of light components reflected by thepolarization beam splitter 33 is reflected by a mirror 37 a of themirror prism 37, and enters the parallel flat plate 38 of an anisotropicoptical crystal. For example, the plate 38 is of lithium niobate (LN), auniaxial anisotropic optical crystal. Laser light incident upon theplate 38 is split into two parts, ordinary and extraordinary rays, byits optical anisotropy with respect to the optic axis of the anisotropicoptical crystal and the appropriate inclination of the optic axis to theincident light. The respective light quantities of the split light beamsin ordinary and extraordinary rays are detected by the second lightreceiving element group 36, which comprises two light receiving elementsformed on the silicon substrate 39. Magneto-optical information isdetected in accordance with the detected light quantities.

[0052] Preferably, the parallel flat plate 38 of LN has a thickness of 2mm to 6 mm. A thickness less than 2 mm is too small to separate thebeams in ordinary and extraordinary rays sufficiently, so that thesignal-to-noise ratio is worsened. Although a thickness greater than 6mm ensures a sufficient distance for separation, it requires the siliconsubstrate 39 to be increased correspondingly in size. In this case, theentire magneto-optical pickup is too large in size to be practical andattain its purpose.

[0053] A parallel flat plate of 4-mm thickness, as a specific example,gives a distance for separation of about 150 mm between the beams inordinary and extraordinary rays. A distance of at least 80 mm should besecured for the separation, depending on the shapes of spots on thelight receiving elements.

[0054] Although the specific values have been given for the thickness ofthe parallel flat plate of LN, a value for the necessary separationdistance is selected as the thickness of the parallel flat plate, whichis formed of any other anisotropic optical crystal than LN, inconsideration of the specific refractive index of the material for theordinary and extraordinary rays. Quartz, KTP, lithium tantalate,calcite, rutile, etc. may be used as the other material than LN. Sincecalcite and rutile are subject to a very great difference in refractiveindex between the ordinary and extraordinary rays, in particular, a longseparation distance can be secured favorably with use of a thicknesssmaller than the thickness of the LN plate.

[0055] In this magneto-optical pickup, the parallel flat plate of theanisotropic optical crystal having a given optic axis direction is usedas a separating optical element for separating magneto-optical signals.Therefore, the pickup requires no adjustment of location of theseparating optical element with respect to the optical axis, so that itcan be assembled efficiently.

[0056] Since the separating optical element comprises a parallel flatplate, which is highly workable and can be adjusted in thickness withhigh accuracy. Thus, the separation distance can be adjusted with veryhigh accuracy.

[0057] Furthermore, separating optical elements of this type can bemass-produced at low cost, since they can be obtained by only cutting awafer-shaped material, e.g., LN, of a given thickness having a givenorientation to pieces of a proper size. In particular, LN is a verysuitable material that is currently mass-produced at very low cost andhas reliable quality and high availability.

[0058] Modification 1

[0059]FIG. 3 shows a modification of the way of mounting the laser lightsource according to the present embodiment. In this modification, asshown in FIG. 3, a laser chip 50, which is equivalent to the laser lightsource 31, is mounted on a silicon substrate 52, which is equivalent tothe silicon substrate 39, through a sub-mount 51. A mirror block 53,which is also mounted the substrate 52, has a mirror surface 53 ainclined at an angle of about 45° to the direction of emission of lightbeams. A light beam emitted from the laser chip 50 is deflected at rightangles to the upper surface of the silicon substrate 52 by the mirrorsurface 53 a of the mirror block 53.

[0060] This arrangement does not require etching or any other work onthe silicon substrate 52, so that it can be manufactured with ease.Besides, the position of an imaginary point of emission as viewed fromabove, that is, a point of reflection of the laser beam on the mirrorsurface 53 a, can be adjusted by shifting the location of the mirrorblock 53. Thus, the mounting accuracy for the laser light source and thelight receiving elements can be eased.

[0061] Modification 2

[0062]FIG. 4 shows a modification of the magneto-optical pickupaccording to the present embodiment. As shown in FIG. 4, thismagneto-optical pickup is formed by additionally providing themagneto-optical pickup of FIG. 1 with a mirror prism 91, a transparentparallel flat plate 92, and a light receiving element 93. The prism 91is bonded to the polarization beam splitter 33. The parallel flat plate92 is located between the prism 91 and the silicon substrate 39. Theflat plate 92 may be in the form of a square pole, such as a rectangularparallelepiped, or a cylinder.

[0063] The magneto-optical pickup has a third optical path, and thepolarization beam splitter 33 separates some components of the lightbeam emitted from the laser light source 31. The separated lightcomponents travel along the third optical path to the light receivingelement 93. The mirror prism 91 and the parallel flat plate 92 guide thelight components separated by the beam splitter 33 to the element 93.

[0064] The light receiving element 93 for monitoring the output of thelaser light source 31 is formed on the silicon substrate 39, on whichthe light receiving element group 34 and 35 and the second lightreceiving element group 36 are formed. Thus, the light receiving element93 is situated flush with the first and second light receiving elementgroups 34, 35 and 36.

[0065] Some light components of the light beam emitted from the laserlight source 31 are reflected by the polarizing film 33 a of thepolarization beam splitter 33 and then by a mirror surface 91 a of themirror prism 91. Then, the light components are transmitted through theparallel flat plate 92 and applied to the light receiving element 93 onthe silicon substrate 39. The element 93 outputs a signal correspondingto the quantity of the incident light. The output of the laser lightsource 31 is controlled in response to the output signal.

[0066] According to this modification, detection of the output of thelaser light source, besides the detection of error signals andmagneto-optical signals, can be effected with use of only a small numberof components. All the necessary functions of the magneto-optical pickupcan be fulfilled with use of a high-quality compact configuration.

[0067] Preferably, the parallel flat plate 92 should be made of glasshaving an appropriate refractive index, or basically, a high refractiveindex. This is because light incident upon the flat plate 92 of ahigh-refraction material is totally reflected by a side face of theplate 92 without substantially leaking out, so that it reaches any otherlight receiving element than the light receiving element 93 as straylight and produces no noises. It is to be understood that the sameadvantage can be also obtained by applying a reflective paint or someother light screen coating to the side face of the parallel flat plate92 instead of using a high-refraction material for the plate 92.

[0068] Further, the parallel flat plate 92 is expected to be as thick asthe parallel flat plate 38 of the anisotropic optical crystal so thatthe efficiency of assembly is improved. More specifically, themagneto-optical pickup can be assembled by only arranging the parallelflat plates 38 and 92 on the silicon substrate 39 and bonding a prismblock group, which is formed by previously uniting the polarization beamsplitter 33 and the mirror prisms 37 and 91, to the respective upperends of the plates 38 and 92. Further, the durability of the pickup toresist heat, vibration, and shock is improved.

[0069] Second Embodiment

[0070] A magneto-optical pickup according to a second embodiment willnow be described with reference to FIGS. 5A, 5B and 5C. Basically, thepickup of the present embodiment has the same configuration as themagneto-optical pickup of the first embodiment. In these drawings,however, the polarization beam splitter and the mirror prism block groupare not shown.

[0071] As shown in FIG. 5A, the magneto-optical pickup according to thesecond embodiment comprises a laser light source 41 for emitting a lightbeam for information reproduction, first light receiving element group,which includes light receiving elements 44 and 45, for detecting errorsignals, and a second light receiving element group 48 for detectingmagneto-optical signals.

[0072] The first light receiving element group 44 and 45 and the secondlight receiving element group 48 are formed on one light receivingelement substrate 43. The substrate 43 is formed in the shape of a U byetching. It is placed on a U-shaped spacer 42 for height adjustment. Thespacer 42 is formed of an insulator, which has a metal film on its uppersurface. The substrate 43 is connected electrically to the metal film ofthe spacer 42, and its backward bias is fetched from an exposed surfaceof the spacer 42.

[0073] The laser light source 41 is mounted on the substrate 43 througha sub-mount 40 so as to emit a light beam in the direction normal to theupper surface of the silicon substrate 43. The point of emission of thelight source 41 is situated substantially on a straight line thatconnects the respective centers of the light receiving elements 44 and45. The center of the second light receiving element group 48 issituated substantially on a straight line that extends at right anglesto the straight line connecting the respective centers of the lightreceiving elements 44 and 45 and passes through the point of emission ofthe laser light source 41.

[0074] As shown in FIG. 5B, the magneto-optical pickup has a transparentflat plate 46 located above the laser light source 41. The flat plate 46is provided with a diffraction grating 46 a for diffracting return lightfrom a storage medium and directing −1st and +1st order diffracted lightbeams toward the light receiving elements 44 and 45, respectively.

[0075] As shown in FIG. 5C, moreover, the magneto-optical pickupcomprises a parallel flat plate 47 of an anisotropic optical crystal,which is located on the second light receiving element group 48. Theplate 47, like the parallel flat plate 38 of the first embodiment,serves to split incident light into ordinary and extraordinary rays.

[0076] The light beam emitted from the laser light source 41 istransmitted through the diffraction grating 46 a, then passes throughthe polarization beam splitter (not shown) and a collimating lens (notshown), and is converged on the information storage medium (not shown)by an objective lens (not shown).

[0077] The return light from the information storage medium, loaded withinformation, having passed through the objective lens and thecollimating lens, reaches at the polarization beam splitter. Somecomponents of the return light are reflected by the polarization beamsplitter, while the remaining components of the return light aretransmitted through the splitter.

[0078] The light components transmitted through the polarization beamsplitter are diffracted by the diffraction grating 46 a, therefore twobeams of −1st and +1st order diffracted light appear. The respectivequantities of the −1st and +1st order diffracted light beams aredetected by the light receiving elements 44 and 45, and error signalsare detected in accordance with the detected quantities.

[0079] On the other hand, the light components reflected by thepolarization beam splitter reflected by a mirror prism (not shown) areseparated into ordinary and extraordinary rays by the parallel flatplate 47 of the anisotropic optical crystal. The respective quantitiesof the split ordinary and extraordinary rays are detected by the lightreceiving element group 48 comprising at least two light receivingelements. Magneto-optical information is detected in accordance with thedetected light quantities.

[0080] The magneto-optical pickup of the present embodiment is highlyproductive because it can be obtained by only additionally providing aconventional package of a semiconductor laser and a light source withlight receiving elements, diffraction grating, polarization beamsplitter, and parallel flat plate of an anisotropic optical crystal.Since the laser light source can be mounted by using existing equipment,in particular, the pickup can be produced at low cost.

[0081] Third Embodiment

[0082]FIG. 6 shows the peripheral portion of a laser light source of amagneto-optical pickup according to a third embodiment. The pickup ofthe present embodiment, which has basically the same configuration asthe first embodiment, is additionally provided with a function to detectthe output of the laser light source.

[0083] As shown in FIG. 6, a laser light source 60 is mounted on asilicon substrate 62 through a sub-mount 61. The magneto-optical pickupcomprises a light receiving element 63, which is formed on the substrate62, for monitoring the output of the light source 60.

[0084] A prism 64, which is located on the light receiving element 63,has a half-mirror surface 64 a inclined at about 45° to the direction ofemission of light beams from the laser light source 60. The surface 64 atransmits some light components of a light beam emitted from the lightsource 60 and reflects the remaining light components at right angles tothe upper surface of the silicon substrate 62. Thus, the half-mirrorsurface 64 a separates some light components of the light beam emittedfrom the light source 60, and the separated light components travelthrough the prism 64 to the light receiving element 63.

[0085] Some light components of the light beam emitted from the laserlight source 60 are transmitted through the half-mirror surface 64 a ofthe prism 64 and applied to the light receiving element 63. The element63 outputs a signal corresponding to the quantity of the incident light,and the signal is used to control the light source 60. As described inconnection with the first embodiment, on the other hand, the lightcomponents reflected by the half-mirror surface 64 a of the prism 64 areconverged on the information storage medium, and the resulting returnlight from the information storage medium is used to detect errorsignals and magneto-optical signals.

[0086] This magneto-optical pickup, besides having the advantage of thefirst embodiment, can detect the output of the laser light source 60without being separately provided with a beam splitter or lightreceiving element. Thus, the pickup can be reduced in size and loweredin cost.

[0087] Modification

[0088]FIG. 7 shows a modification of the magneto-optical pickupaccording to the present embodiment. As shown in FIG. 7, a laser lightsource 70 is mounted on a sub-mount 71 located on a silicon substrate72. The pickup further comprises a light receiving element 73 formonitoring the output of the light source 70. The element 73 is formedon the substrate 72, which has a light receiving element group 76 fordetecting magneto-optical signals. The substrate 72 further has a lightreceiving element group (not shown) for detecting error signals. Theselight receiving element groups are arranged in the same manner as theones according to the second embodiment.

[0089] A prism 74, which is located on the light receiving element 73,has a half-mirror surface 74 a inclined at about 45° to the direction ofemission of light beams from the laser light source 70. The surface 74 atransmits some light components of a light beam emitted from the lightsource 70 and reflects the remaining light components at right angles tothe upper surface of the silicon substrate 72. Thus, the half-mirrorsurface 74 a separates some light components of the light beam emittedfrom the light source 70, and the separated light components travelthrough the prism 74 to the light receiving element 73.

[0090] The prism 74 is overlain by a transparent flat plate 77, whichhas a diffraction grating 77 a for diffracting the return light from theinformation storage medium and directing its −1st and +1st orderdiffracted light beams toward light receiving elements of the lightreceiving element group for error signal detection. The flat plate 77 isoverlain by a polarization beam splitter 78, which transmits some lightcomponents of the return light from the storage medium and reflects theremaining light components. Bonded to the beam splitter 78 is a mirrorprism 79, which deflects the reflected light components toward the lightreceiving element group 76 for magneto-optical signal detection.

[0091] A parallel flat plate 75 of an anisotropic optical crystal forseparating beams in ordinary and extraordinary rays is located on thelight receiving element group 76. The flat plate 75 is formed previouslyhaving a mirror surface 75 a on its face, which is bonded to the prism74. The mirror surface 75 a serves to prevent light propagating in theprism 74 from getting into the flat plate 75, thereby restraining the SNratio of recorded information from lowering. Thus, the parallel flatplate 75 may be formed previously having a light shielding film bypainting or coating instead of the mirror surface 75 a.

[0092] The prism 74 and the parallel flat plate 75 are previously bondedto each other before they are mounted on the silicon substrate 72, so asto form a trapezoid block. This trapezoid block can be manufactured withhigh efficiency by, for example, bonding a prism-shaped anisotropicoptical crystal and a triangular half-mirror prism and then cutting theresulting structure at given intervals.

[0093] The mirror surface 75 a of the parallel flat plate 75 is formedbefore the prism 74 and the plate 75 are bonded to each other, wherebythe incidence of mistakes in orientation for the bonding operation canbe lowered. The block including the prism 74 and the flat plate 75bonded to each other serves to facilitate handling for its mounting onthe silicon substrate 72 and lower the possibility of wrongly directedmounting of the plate 75 on the substrate 72.

[0094] Fourth Embodiment

[0095]FIG. 8 shows a magneto-optical pickup according to a fourthembodiment. The pickup of the present embodiment has basically the sameconfiguration as the second embodiment.

[0096] A laser light source 80 is mounted on a sub-mount 81 located on asilicon substrate 82. The substrate 82 is provided with a lightreceiving element group (not shown) for detecting error signals and alight receiving element group 87 for detecting magneto-optical signals.These light receiving element groups are arranged in the same manner asthe ones according to the second embodiment.

[0097] A trapezoid block 83 of an anisotropic optical crystal is locatedon the silicon substrate 82. The block 83 has a parallel flat plateportion, which is situated on the light receiving element group 87 formagneto-optical signal detection.

[0098] The block 83 has a mirror surface 83 a inclined at about 45° tothe direction of emission of light beams from the laser light source 80.The mirror surface 83 a reflects a light beam from the light source 80in the direction normal to the silicon substrate 82. The mirror surface83 a is formed, for example, by first coating chromium (Cr) and thencoating gold (Au) over the inclined side of the block 83.

[0099] The mirror surface 83 a is overlain by a transparent flat plate84, which has a diffraction grating 84 a for diffracting return lightfrom an information storage medium and directing its −1st and +1st orderdiffracted light beams toward light receiving elements of the lightreceiving element group for error signal detection. The flat plate 84 isoverlain by a polarization beam splitter 85, which transmits some lightcomponents of the return light from the storage medium and reflects theremaining light components. Bonded to the beam splitter 85 is a mirrorprism 86, which deflects the reflected light components toward the lightreceiving element group 87 for magneto-optical signal detection.

[0100] As mentioned before, the parallel flat plate portion of thetrapezoid block 83 of the anisotropic optical crystal is situated on thelight receiving element group 87. This flat plate portion has an opticaxis inclined at 45° to the optical axis, and serves to separateincident light from the mirror prism 86 into ordinary and extraordinaryrays.

[0101] In FIG. 8, the light beam emitted from the laser light source 80is reflected by the mirror surface 83 a and transmitted through thetransparent flat plate 84 having the diffraction grating 84 a and thepolarization beam splitter 85. Thereafter, the light beam passingthrough a collimating lens (not shown) is converged on the informationstorage medium (not shown) by an objective lens (not shown).

[0102] The return light from the information storage medium, loaded withinformation, having passed through the objective lens and thecollimating lens, reaches at the polarization beam splitter 85. Somecomponents of the return light are reflected by the polarization beamsplitter 85, while the remaining components of the return light aretransmitted through the splitter 85.

[0103] The light components transmitted through the polarization beamsplitter are diffracted by the diffraction grating 84 a of thetransparent flat plate 84, therefore two beams of −1st and +1st orderdiffracted light appear. The respective quantities of the −1st and +1storder diffracted light beams are detected by the light receivingelements of the light receiving element group for error signaldetection, and error signals are detected in accordance with thedetected quantities.

[0104] On the other hand, the light components reflected by thepolarization beam splitter 85 reflected by a mirror surface 86 a of themirror prism 86 are separated into ordinary and extraordinary rays bythe parallel flat plate portion of the block 83 of the anisotropicoptical crystal. The respective quantities of the separated ordinary andextraordinary rays are detected by the light receiving element group 87for magneto-optical signal detection. Magneto-optical information isdetected in accordance with the detected light quantities.

[0105] In this magneto-optical pickup, the trapezoid block 83 combines afunction to deflect vertically a light beam emitted parallel to theupper surface of the silicon substrate 82 and a function to separatereturn light into ordinary and extraordinary rays for detection ofmagneto-optical signals, so that the number of components used in thepickup can be reduced. Since the block 83 has an appropriate size,moreover, handling for its mounting on the substrate 82 is easy, andpositioning can be carried out with ease.

[0106] Fifth Embodiment

[0107] A packaged magneto-optical pickup according to a fifth embodimentwill now be described with reference to FIG. 9. Although themagneto-optical pickup of FIG. 4 is illustrated in FIG. 9, the packagedpickup may be any of the magneto-optical pickups described above.Preferably, the pickup should have a mechanism for monitoring the lightquantity of the light source, in particular.

[0108] As shown in FIG. 9, the magneto-optical pickup is placed on apackage base 100 and sealed by a cap 101 having a glass window 102.

[0109] Electrode pins 103, which are fixed to the base 100 by aninsulator 104, are used to supply electric power to light emittingelements and fetch electric information from light receiving elements.

[0110] A sealed internal space defined by the base 100 and the cap 101is filled with an inert gas, such as nitrogen or argon, so that it isprotected against external penetration of water or oxygen.

[0111] According to the packaged magneto-optical pickup of the presentembodiment, the ambiance of the light emitting elements, in particular,is replaced with the inert gas, so that the light emitting elements canbe prevented from being deteriorated or damaged by oxygen or water.Thus, the light emitting elements can enjoy long life. Since the entireunit including the light emitting elements, a beam splitter, lightreceiving elements, etc. is hermetically sealed by an integral package,moreover, the internal elements can enjoy a very high degree of freedomof layout. Since highly sophisticated optical elements are not exposedto the outside, furthermore, they cannot be damaged when they areincorporated into an optical disk apparatus. If the optical elements aresoiled, moreover, they can be washed. Besides, an adhesive that is usedin assembling the optical elements can be prevented from being expandedor deformed by water, so that fixed optical properties can bemaintained.

[0112] Sixth Embodiment

[0113] A magneto-optical pickup according to a sixth embodiment will nowbe described with reference to FIG. 10. The present embodiment isconstructed in the same manner as the first embodiment, while acomposite polarization beam splitter prism 114 comprising a triangularprism and a parallelogrammatic prism is used in place of thepolarization beam splitter 33 and the mirror prism 37. The prism 114 hasa polarizing film 114 a and a reflective surface 114 b coated with amulti-layer film for phase control. TABLE 1 shows the properties of themulti-layer film of the reflective surface 114 b. TABLE 1 Film thicknessRefractive Layer Material (nm) index 0 Glass 1.62 1 SiO₂ 131 1.46 2 TiO₂ 31 2.25 3 SiO₂ 120 1.46 4 TiO₂  68 2.25 5 SiO₂ 139 1.46 6 TiO₂  46 2.257 Air 1.00

[0114] Although the present embodiment has basically the same functionsas the first embodiment, it additionally has the following functions andeffects.

[0115] The light totally reflected by the reflective surface 114 bgenerally has a great phase difference between p-polarized light ands-polarized light, which are polarized at right angles to each other.Such phase difference unfortunately lower the signal quality.

[0116] The phase difference varies depending on the incident angle uponthe reflective surface, in particular. If the convergent beam of lightis totally reflected, as in the case of the present invention,therefore, the variation of the phase difference depending on theincident angle is greater, so that the signal quality is influenced morestrongly. According to the present embodiment, however, the reflectivesurface 114 b is coated with the multi-layer film shown in TABLE 1 tocontrol the phase difference, so that the phase difference is reducedsubstantially to zero, and its variation depending on the incident angleof light upon the reflective surface can be controlled or suppressedsatisfactorily. FIG. 11 shows generation of the phase difference.

[0117] According to the present embodiment, in contrast with the casewhere the multi-layer film (coat) is not used, the phase difference issubstantially zero, and it hardly varies depending on the incidentangle.

[0118] Since there is no substantial phase difference between thep-polarized light and s-polarized light on the reflective surface 114 baccording to the present embodiment, in particular, magneto-opticalsignals can be detected highly satisfactorily.

[0119] Although several embodiments have been described specificallyherein with reference to the accompanying drawings, the presentinvention is not limited to those embodiments, therefore, variouschanges and modifications may be effected therein.

[0120] According to any of the embodiments described above, for example,the polarization beam splitter and the mirror prism are cubicstructures. Alternatively, however, they may be formed by combing atriangular prism and a parallelogrammatic prism. Further, the packageand the cap may be formed of a metal, resin, or ceramics.

[0121] The magneto-optical pickup of the present invention may beapplied to a finite optical system in which emitted light is convergeddirectly on an information storage medium by an objective lens withoutusing a collimating lens or an infinite optical system in which light isconverged by an objective lens after it is temporarily collimated by acollimating lens.

[0122] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A magneto-optical pickup having first and secondoptical paths, comprising: a light source for emitting a light beam, thelight beam traveling to an information recording medium along the firstoptical path; a first light receiving element group for detecting anerror signal; a second light receiving element group for detecting amagneto-optical signal, the first and second light receiving elementgroups being situated substantially on one plane; a diffraction gratingfor diffracting light returned along the first optical path from theinformation storage medium, the diffracted light being directed towardthe first light receiving element group; a polarization beam splitterfor separating a part of the return light from the information storagemedium, a beam of the separated part of return light traveling to thesecond light receiving element group along the second optical path; amirror for bending the second optical path, the light beam reflectedthereby being directed toward the second light receiving element group;and an anisotropic optical crystal member having an optic axis inclinedto the optical axis at an angle within the range between 30° and 60°,the crystal member including a substantially flat parallel plateportion, for splitting the reflected light beam from the mirror into aplurality of split light beams and directing the split light beamstoward the second light receiving element group.
 2. A magneto-opticalpickup according to claim 1, wherein the anisotropic optical crystalmember is of lithium niobate, and the substantially parallel flat plateportion has a thickness of 2 mm to 6 mm.
 3. A magneto-optical pickupaccording to claim 1, wherein the first light receiving element groupincludes two light receiving elements for receiving beams of −1st orderdiffracted light and +1st order diffracted light, which are diffractedby the diffraction grating, respectively, and the light source islocated halfway between the two light receiving elements and emits thelight beam at right angles to the one plane.
 4. A magneto-optical pickupaccording to claim 1, wherein the light source emits the light beamparallel to the one plane, and the pickup further comprises a mirror fordeflecting the light beam from the light source at right angles to theone plane.
 5. A magneto-optical pickup according to claim 1, wherein thepickup, which has a third optical path, further comprises a third lightreceiving element for monitoring the output of the light source, thethird light receiving element being situated substantially on the sameplane as the first and second light receiving element groups andoutputting a signal corresponding to the quantity of incident light, thesignal being used to control the light source, and a separating elementfor separating a part of light from the light source, a beam of theseparated part of light traveling to the third light receiving elementalong the third optical path.
 6. A magneto-optical pickup according toclaim 5, wherein the polarization beam splitter serves also as theseparating element, the separated light beam being directed parallel tothe one plane, and the pickup further comprises a mirror for bending thethird optical path, a beam of the light reflected thereby being directedtoward the third light receiving element, a transparent member includinga substantially parallel flat plate portion, the substantially parallelflat plate portion being between the mirror for bending the thirdoptical path and the third light receiving element, the substantiallyparallel flat plate portion of the transparent member being as thick asthe substantially parallel flat plate portion of the anisotropic opticalcrystal member.
 7. A magneto-optical pickup according to claim 5,wherein the light source emits the light beam parallel to the one plane,and the pickup further comprises a half-mirror for deflecting the lightbeam from the light source at right angles to the one plane, and a prismhaving a side on which the half-mirror is formed, the half-mirrorserving also as the separating element, and the prism being located onthe third light receiving element.
 8. A magneto-optical pickup accordingto claim 7, wherein the prism and the anisotropic optical crystal memberare previously bonded to form an integral structure.
 9. Amagneto-optical pickup according to claim 8, wherein the anisotropicoptical crystal member has a mirror surface previously formed on theside thereof to which the prism is bonded.
 10. A magneto-optical pickupaccording to claim 8, wherein the anisotropic optical crystal member hasa shielding film previously formed on the side thereof to which theprism is bonded.
 11. A magneto-optical pickup according to claim 7,wherein the anisotropic optical crystal member has a slanting side faceinclined at 45° to the one plane, and the half-mirror is formed on theslanting side face of the crystal member.
 12. A magneto-optical pickupaccording to claim 1, wherein the mirror for bending the second opticalpath has a phase control multi-layer film for reducing a phasedifference between two polarized light components, which are polarizedat right angles each other, substantially to zero throughout theeffective range of the incident angle.
 13. A magneto-optical pickupaccording to claim 1, further comprising a package for sealing all ofthe elements, i.e., the light source, first light receiving elementgroup, second light receiving element group, diffraction grating,polarization beam splitter, mirror, and anisotropic optical crystalmember, the internal space of the package being filled with an inertgas.
 14. A magneto-optical pickup according to claim 5, furthercomprising a package for sealing all of the elements, i.e., the lightsource, first light receiving element group, second light receivingelement group, diffraction grating, polarization beam splitter, mirror,and anisotropic optical crystal member, the internal space of thepackage being filled with an inert gas.